TABLE 3.
Results of subgroup analyses in the meta‐analyses of correlation coefficients
| Moderator | k cohorts | I 2 (%) | Pooled r | 95% CI | Q between | P‐value | |
|---|---|---|---|---|---|---|---|
| HairF versus BMI | QUIPS 1: Study participation (population‐based sampling) | 0.34 | 0.55 | ||||
| Yes | 34 | 51 | 0.10 | 0.07; 0.13 | |||
| No | 88 | 51 | 0.11 | 0.08; 0.14 | |||
| QUIPS 3: Prognostic factor measurement (HairGC analysis method) | 0.05 | 0.98 | |||||
| LC–MS | 47 | 51 | 0.10 | 0.07; 0.14 | |||
| ELISA | 52 | 35 | 0.10 | 0.07; 0.14 | |||
| CLIA | 21 | 66 | 0.11 | 0.05; 0.17 | |||
| QUIPS 4: Outcome (anthropometric) measurement | 14.34 | <0.001 | |||||
| Self‐reported | 67 | 22 | 0.15 | 0.12; 0.18 | |||
| Objectively measured | 55 | 62 | 0.07 | 0.04; 0.10 | |||
| QUIPS 5: Study confounding | 2.74 | 0.43 | |||||
| CS use and outliers handled | 39 | 62 | 0.13 | 0.09; 0.17 | |||
| Only outliers handled | 22 | 29 | 0.09 | 0.05; 0.13 | |||
| Only CS use handled | 33 | 30 | 0.10 | 0.06; 0.15 | |||
| Neither handled | 28 | 51 | 0.08 | 0.03; 0.12 | |||
| QUIPS 6: Statistical analysis (Relevant statistics fully reported) | 0.01 | 0.93 | |||||
| Yes | 118 | 50 | 0.10 | 0.08; 0.13 | |||
| No | 4 | 65 | 0.10 | −0.04; 0.23 | |||
| HairF versus BMI SDS | QUIPS 1: Study participation (population‐based sampling) | 0.12 | 0.73 | ||||
| Yes | 4 | 0 | 0.14 | 0.01; 0.27 | |||
| No | 7 | 0 | 0.12 | 0.05; 0.18 | |||
| QUIPS 3: Prognostic factor measurement (HairGC analysis method) | 0.63 | 0.73 | |||||
| LC–MS | 6 | 70.7 | 0.06 | −0.13; 0.25 | |||
| ELISA | 3 | 0 | 0.07 | −0.13; 0.26 | |||
| CLIA | 2 | 0 | 0.13 | 0.04; 0.21 | |||
| QUIPS 4: Outcome (anthropometric) measurement | 2.11 | 0.15 | |||||
| Self‐reported | 4 | 0 | 0.14 | 0.08; 0.20 | |||
| Objectively measured | 7 | 32.1 | −0.01 | −0.19; 0.18 | |||
| QUIPS 5: Study confounding | 0.86 | 0.83 | |||||
| Both handled | 2 | 0 | 0.13 | 0.03; 0.24 | |||
| Only outliers handled | 2 | 0 | 0.13 | 0.04; 0.21 | |||
| Only CS use handled | 5 | 60.8 | −0.01 | −0.31; 0.28 | |||
| Neither handled | 2 | 0 | 0.13 | 0.00; 0.26 | |||
| HairF versus WC | QUIPS 1: Study participation (population‐based sampling) | 3.95 | 0.05 | ||||
| Yes | 9 | 65 | 0.07 | 0.02; 0.13 | |||
| No | 15 | 60 | 0.15 | 0.09; 0.20 | |||
| QUIPS 3: Prognostic factor measurement (HairGC analysis method) | 0.17 | 0.92 | |||||
| LC–MS | 12 | 78 | 0.11 | 0.05; 0.18 | |||
| ELISA | 7 | 4 | 0.10 | 0.02; 0.17 | |||
| CLIA | 5 | 77 | 0.11 | 0.02; 0.21 | |||
| QUIPS 4: Outcome (anthropometric) measurement | 0.67 | 0.41 | |||||
| Self‐reported | 3 | 40 | 0.18 | 0.01; 0.35 | |||
| Objectively measured | 21 | 71 | 0.11 | 0.06; 0.15 | |||
| QUIPS 5: Study confounding | 5.90 | 0.12 | |||||
| Both handled | 9 | 68 | 0.08 | 0.02; 0.15 | |||
| Only outliers handled | 3 | 0 | 0.16 | 0.13; 0.19 | |||
| Only CS use handled | 7 | 33 | 0.13 | 0.05; 0.21 | |||
| Neither handled | 5 | 77 | 0.10 | −0.03; 0.23 | |||
| HairF versus WHR | QUIPS 1: Study participation (population‐based sampling) | 0.56 | 0.46 | ||||
| Yes | 4 | 57 | 0.15 | 0.03; 0.26 | |||
| No | 12 | 36 | 0.10 | 0.04; 0.15 | |||
| QUIPS 3: Prognostic factor measurement (HairGC analysis method) | 0.34 | 0.56 | |||||
| LC–MS | 11 | 33 | 0.10 | 0.05; 0.15 | |||
| ELISA | 4 | 76 | 0.16 | −0.03; 0.34 | |||
| QUIPS 4: Outcome (anthropometric) measurement | 5.79 | 0.02 | |||||
| Self‐reported | 2 | 0 | 0.36 | 0.16; 0.53 | |||
| Objectively measured | 14 | 36 | 0.10 | 0.06; 0.14 | |||
| QUIPS 5: Study confounding | 2.85 | 0.24 | |||||
| Both handled | 6 | 53 | 0.09 | 0.02; 0.15 | |||
| Only outliers handled | 5 | 0 | 0.13 | 0.10; 0.16 | |||
| Only CS use handled | 4 | 57 | 0.23 | 0.06; 0.38 | |||
| Neither handled | 1 | NA | NA | NA | |||
| HairE versus BMI | QUIPS 1: Study participation (population‐based sampling) | 0.02 | 0.89 | ||||
| Yes | 6 | 40 | 0.11 | 0.07; 0.15 | |||
| No | 9 | 46 | 0.12 | 0.02; 0.21 | |||
| QUIPS 4: Outcome (anthropometric) measurement | 0.24 | 0.62 | |||||
| Self‐reported | 3 | 78 | 0.22 | −0.20; 0.57 | |||
| Objectively measured | 12 | 59 | 0.12 | 0.07; 0.16 | |||
| QUIPS 5: Study confounding | 8.08 | 0.04 | |||||
| Both handled | 4 | 55 | 0.16 | 0.11; 0.21 | |||
| Only outliers handled | 4 | 0 | 0.07 | 0.04; 0.11 | |||
| Only CS use handled | 5 | 0 | 0.09 | −0.02; 0.20 | |||
| Neither handled | 2 | 61 | 0.05 | −0.12; 0.21 | |||
Note: Subgroup analyses were only performed when data of at least 2 cohorts were available within a subgroup and 10 cohorts across all subgroups. Bold text indicates statistically significant effect (P‐value < 0.05).
Abbreviations: CI, confidence interval; HairF, hair cortisol; SDS, standard deviation score; WC, waist circumference; WHR, waist‐to‐hip ratio; LC–MS, liquid chromatography‐(tandem) mass spectrometry; ELISA, enzyme‐linked immunosorbent assay; CLIA, chemiluminescent immunoassay.